This invention relates generally to the field of electro-optics and, more particularly, to electro-optics involved in target detection techniques.
In developing systems to optically detect targets, problems are encountered when the target appears amid a background of clouds. In such situations, tradeoffs must be made in order to obtain a sufficient signal-to-background ratio that will allow detection. The signal-to-background ratio corresponds to a signal-to-noise ratio in electrical devices. The bandwidth in which the system operates should also be examined to maximize performance. Three elements must be considered in bandwidth optimization. These are (1) spectral characteristics of the target, (2) spectral characteristics of the cloud background, and (3) atmospheric transmission and spectral characteristics of the background in the absence of clouds. The current infrared frequency band was chosen primarily to provide adequate signal strength while minimizing the background cloud return. The present art consists of a group of sensors capable of a certain degree of signal-to-background detection within a specified bandwidth feeding their information into an electronic network for signal processing.
One apparatus for the resolution of targets in the presence of clutter is described in U.S. Pat. No. 3,946,382. Another apparatus for identifying a target by recognizing its radar signature and separating this signature from background clutter is taught in U.S. Pat. No. 4,001,820. Both of these apparatus are specifically directed to radar signals and both involve a comparison with a threshold. The present invention on the other hand relates to video signals in general and involves more than one spectral bandwidth.